Field of the Invention
The present disclosure relates to wireless power transmission.
Description of the Related Art
Conventionally, a wireless power transmission system has been known which includes a power transmission apparatus configured to wirelessly transmit power and a power reception apparatus configured to receive the power supplied from the power transmission apparatus. In the wireless power transmission system, when an object exists within a power transmission service area covered by the power transmission apparatus, the object is influenced by an electromagnetic wave which is output, to supply power, by the power transmission apparatus. In the wireless power transmission system, therefore, it is necessary to detect an object that does not have a power reception function and that exists in the power transmission service area covered by the power transmission apparatus (hereinafter such an object will be referred to as a foreign object). Japanese Patent Laid-Open No. 2010-220418 discloses a technique in which a power reception apparatus makes a comparison between the magnitude of a current flowing through a transmission antenna represented by information received from the power transmission apparatus and the magnitude of a current flowing through a battery when the battery is charged using received power. When the ratio of the magnitude of the current flowing through the battery to the magnitude of the current flowing through the transmission antenna is smaller than a particular value determined based on a particular energy conversion efficiency, the power reception apparatus determines that there is a foreign object.
In the technique disclosed in Japanese Patent Laid-Open No. 2010-220418, the foreign object detection is realized by comparing the magnitude of the current flowing through the transmission antenna and the magnitude of the current flowing through the battery being charged with the received power. However, in the technique disclosed in Japanese Patent Laid-Open No. 2010-220418, there is a possibility that it is difficult to correctly detect a foreign object in a situation in which a change occurs in consumption power of a load that consumes received power. For example, in a case where a motor is a load that consumes received power and the rotation speed of the motor varies, when the rotation speed of the motor is reduced, the consumption power of the motor decreases, and thus the current flowing through the motor decreases. In the technique disclosed in Japanese Patent Laid-Open No. 2010-220418, when a reduction occurs in the current flowing through the load consuming the received power, there is a possibility that it is determined incorrectly that there is a foreign object in a situation in which there is actually no foreign object in the power transmission service area.
As described above, in the technique disclosed in Japanese Patent Laid-Open No. 2010-220418, when consumption power of a load changes, it is difficult to distinguish whether the change in the current is caused by the change in the consumption power of the load or existence of a foreign object, and thus there is a possibility that it is difficult to correctly determine whether there is a foreign object in the power transmission service area.